High density storage disks are configured with layers of materials that provide the required data stability for storage. The magnetic properties of the media may be softened when writing to the disk to assist changing the bit state. Energy Assisted Magnetic Recording (EAMR) device or Heat Assisted Magnetic Recording (HAMR) technology provides heat that is focused on a nano-sized bit region when writing onto a magnetic storage disk, which achieves the magnetic softening. A light waveguide directs light from a laser diode to a near field transducer (NFT). The NFT couples the diffraction limited light from waveguide (WG), then further focuses the light field energy beyond diffraction limit down to a highly concentrated (nano-sized) near-field media heating spot enabling EAMR/HAMR writing to the magnetic storage disk. Inefficiencies in the NFT can have a negative impact on the power budget of the laser diode and the EAMR/HAMR system lifetime. Higher NFT efficiency allows for lower laser power demand, relieving EAMR/HAMR system requirement on the total optical power from the laser source, and results in less power for parasitic heating of the EAMR/HAMR head resulting for improved reliability.
In an NFT, plasmonic metal can be used to form SPPs (surface plasmon polaritons), which carry out the nano-focusing function beyond the light's diffraction limit. High quality plasmonic metals rely on high density free electrons which have weak mechanical robustness, and are susceptible to damages caused by thermal or mechanical stresses in an EAMR head. Under these stresses, the service lifetime of the EAMR/HAMR device is limited to NFT failure occurring at the plasmonic metal part having fine (nano-sized) features, such as at a ridge or a pin.